Method and device in tractor-trailer brakes

ABSTRACT

The invention relates to a method and a device for controlling the operating brake pressure to pressure medium brakes in a vehicle combination comprising a tractor vehicle and at least one trailer vehicle. The vehicles in this case are connected by a conventional coupling device that includes standard brakeline connections. Forces developing in the coupling device are measured during the course of braking and are reduced to a predetermined value by adjusting the brake pressure for at least the brakes of the trailer vehicle in dependence on the longitudinal inclination of the tractor vehicle and of the actual deceleration thereof. The adjusted value of the brake pressure is retained for the purpose of being the starting value at the next braking of the vehicles.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method and a device for controlling theoperating brake pressure for pressure medium brakes in a vehiclecombination comprising a tractor vehicle and at least one trailervehicle, said vehicles being connected by a conventional couplingdevice, according to which the driver of said tractor vehicle generatesby means of a brake valve an operating pressure defining the brakepressure of said tractor and trailer vehicle, forces developing in saidcoupling device being measured during the course of braking and beingreduced to a predetermined value.

2. Description of the Related Art

The brakes of a trailer vehicle in a vehicle combination are adjusted soas to function in a satisfying way when the trailer vehicle is fullyloaded. National laws and regulations stating the lowest decelerationwhich the vehicle combination has to fulfil when braking must also becomplied with. In practice this means that certain problems arise whenthe trailer vehicle is uncompletely loaded or when it is not loaded atall. The problems arising are for instance wheel locking when braking,brake overheating, unnecessary wearing of the brake lining of thetrailer vehicle brakes and on the coupling device between said tractorand trailer vehicle, etc.

To overcome these problems it is suggested in SE 455 854 to provide inthe coupling between said tractor and trailer vehicle a transducer forindicating pulling and pushing, respectively, of the coupling and thatsaid transducer is operatively connected through a central unit to avalve for controlling the brake pressure to the brakes of said trailervehicle. The control of the brake pressure is made through the servicebrake system of the tractor vehicle and is thus comparatively slow.Furthermore, the control can only take place as a decrease of thepressure existing in the tractor vehicle during the braking Anadjustment which in certain aspects is less favourable can also takeplace when there is a braking on a hill, and in a non-moving vehicle ifthere is a signal received from the transducer while at the same timethe driver presses the brake pedal.

Also other problems may arise in an incorrect distribution of thebraking power between the tractor and the trailer vehicle when thevehicle combination is decelerated. In a tractor vehicle having a lowerbraking power than accepted by law also the braking power of the vehiclecombination will be unsatisfactory and below the accepted. If thebraking ability of the brakes of the tractor vehicle is too low theresult is a pushing trailer vehicle, which may result in so calledjack-knifing Said latter problem is suitably avoided by securing thatthe rear vehicle of the vehicle combination is braked first and thatthere is a certain amount of overcapacity in the brakes of said vehicle.Such a solution was suggested in U.S. Pat. No. 4,231,442, a deviceaccording to said patent comprising a power sensitive transducerarranged in the coupling between said tractor and trailer vehicle, anamplifier, and a switch connected to the brake pedal of said tractorvehicle. When the driver presses said braking pedal the brakes of thetrailer vehicle are first activated. The pulling force thereby appearingin said coupling between the vehicles actuates through said amplifierthe brakes of the tractor vehicle. The amplifier is activated only ifsaid switch has been actuated by said brake pedal. However, there is aconsiderable risk in activating firstly the brakes of said trailervehicle because if said brakes do not work properly the result may bethat the vehicle combination as a whole is not decelerated sufficientlyneither with respect to the actual braking requirement nor with respectto the minimal deceleration prescribed.

To avoid wearing of the tires and to decrease the risk of skidding therehas also been suggested different systems comprising non-locking brakes.However, such systems do not overcome problems with an unnecessarywearing of the brake linings of the trailer vehicle brakes and on thecoupling device between said tractor and trailer vehicle. Also, it isnot possible to avoid problems with increasing differences intemperature between the different wheel brakes of the vehicle units. Ifthe vehicles are provided with pressure brakes there is also a certainunnecessary waste of pressurized air during every course of brakingbecause any excess pressure is ventilated so as to avoid wheel locking.However, non-locking brakes can be an excellent supplement to othertypes of brake control systems.

SUMMARY OF THE INVENTION

An object of the present invention is to overcome generally the problemsand drawbacks mentioned above of previously known brake control systems.Another object of the invention is to secure a high total brakingability of the vehicle combination, to provide the required andprescribed deceleration even if any of the vehicles during operation hasa problem with reduced braking ability.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Now the invention will be described in more detail by means of anembodiment, reference being made to the accompanying drawing, which is aschematic drawing of the device according to the invention

In the coupling between the tractor and the trailer vehicle there isprovided a force sensitive transducer 10, delivering an electric signalin dependence of the force acting on said coupling. The electric signalis fed to a central unit 11 controlling in dependence of said signal andother incoming electric signals the brake pressure of the air pressurebrakes 16A-16D of the trailer vehicle. By means of a brake pedal, whichis provided with a valve 12, said pedal being arranged in the tractorvehicle, the driver of the tractor vehicle controls the brakes 18A-18Dof the tractor vehicle. Between the valve 12 and the brakes there is ina conventional way provided brake valves, said valves not being shown onthe drawing for a reason of clarification of the invention.

The primary side of said valve 12 is connected to a supply container 15,and the secondary side thereof is connected to a pressure sensitivetransducer 20 recording the so called operating pressure, and convertingthe pressure signal to an electric signal, which is supplied to thecentral unit 11. In the tractor vehicle there is provided also anaccelerometer 13 recording the longitudinal inclination in relation tothe horizontal plane of the tractor vehicle and also the accelerationand deceleration, respectively, of the vehicle. The accelerometer can beof a conventional type that converts recorded signals to electricsignals, which are supplied to the central unit 11.

An electrically controlled valve 14 is on the primary side thereofconnected to the supply container 15, and is operatively connected tosaid central unit 11, and receives from said central unit 11 an electriccontrol signal. In dependence of said control signal the pressuresupplied from said supply container 15 is adjusted to the desiredoperating pressure, which is supplied to the brakes 16A-16D of thetrailer vehicle through conventional coupling means between saidvehicles In accordance with the brakes of the tractor vehicle theoperating pressure is utilized to actuate the brakes throughconventional brake valves, not shown here. A compressor 19 maintains thedesired supply pressure in said container 15.

For security reasons a two-way valve 17 is provided between the valve 14and the brakes 16A-16D of the tractor vehicle. The second input of saidtwo-way valve 17 is supplied with operating pressure from said valve 12of the brake. An error condition with any of the more importantcomponents of the device said two-way valve 17 is activated in such away that the brakes of the trailer vehicle are supplied with theoperating pressure of the tractor value by said valve 14. This by-passcan be accomplished also by means of an electric switch provided at thedriver's seat.

The operating pressure line from the two-way valve 17 provided on thetractor vehicle is connected to operating pressure lines on the trailervehicle through conventional connection means 21 between the vehicles.

At the driver's seat there is provided a display 22, which isoperatively connected to said central unit 11, and which receives signalfrom said unit 11 about the present control condition and direction offorces in said coupling device between the tractor and the trailervehicle so as to inform the driver. Any error conditions in the brakesor other relevant parts are stored in the central unit and can be readby means of indicating means that can be connected to said central unit.

Now a braking course on flat ground, that is, when the accelerometer atthe start of the braking does not indicate any inclination, accelerationor deceleration, will be described.

During driving forces in the coupling are continuously recorded by theforce sensitive transducer 10, the actual state of forces being thebasis of the control. When the driver presses the brake pedal said valve12 adjusts in relation to the pressing of the pedal the actual supplypressure to an operating pressure, which is supplied to the pressuresensitive transducer 20 and also to said two-way valve 17. The controlpressure is supplied also directly to the brakes 18A-18D of the tractorvehicle. An increase of the operating pressure over a predeterminedvalue is recorded by the central unit 11, which by a short impulse openscompletely said valve 14 thereby affecting the brakes of the vehicle toinitiate movement towards a brake position. At the same level of theoperating pressure the output of said accelerometer is also recorded. Ifsaid output indicates that the longitudinal axis of said tractor vehicleis not parallel with the horizontal plane, that is the vehicle is in ahill, or if said accelerometer indicates that the vehicle is standingstill no control of the brake pressure to the brakes of the trailervehicle takes place. A previously made adjustment of the brake pressureto the brakes of the trailer vehicle instead remains during thesecircumstances. However, if the tractor vehicle is in a horizontalposition a new control procedure as described below is initiated. If apreviously made adjustment of the brake pressure exists said adjustmentis utilized as a initial value and a corresponding pressure is suppliedto the brakes through said valve 14 and said two-way valve 17.

The force now acting on the coupling between the tractor and the trailervehicle is continuously recorded by the pressure sensitive transducer10. A pulling force indicating a brake power of the tractor vehiclewhich is too large is recorded by the central unit, which decreases theoperating pressure through the valve 14. However, the decrease takesplace only when the vehicle combination is decelerated appropriately.The deceleration is continuously recorded by said accelerometer 13, theoutput thereof being processed by said central unit during the controland brake procedure. When the power acting on the coupling has beendecreased to a predetermined value the control procedure is interruptedand the present value is stored in the central unit. Said value is laterused as an initial value at the next brake procedure.

When pushing is indicated, that is when the brake power of the trailervehicle is too low, said central unit transmits a signal to said valve14 to increase the operating pressure to the brakes of the trailervehicle. As said valve 14 is supplied with supplied pressure theoperating pressure to the brakes of the trailer vehicle can, ifrequired, exceed the operating pressure to the brakes of the tractorvehicle. This is a considerable advantage because normally there arepressure losses in operating pressure lines of the tractor vehicle, saidlosses decreasing the available pressure interval.

To achieve the prescribed deceleration higher pulling forces are allowedin the coupling even though the wear thereof is increased However, sucha control condition depends on a malfunction of the brakes of thetractor vehicle, and such a condition is stored in the central unit asdescribed above.

In respect of the present control condition of the brake pressure thereis a reset of the central unit each time the driver brakes the vehiclewith the parking brake. Thus, the next braking procedure is started witha non-adjusted operating pressure, that is the same control pressure tothe brakes of the trailer vehicle as to the brakes of the tractorvehicle.

The by-passing of said valve 14 resulting in that the operating pressureof the tractor vehicle instead is supplied to the brakes through saidtwo-way valve 17 and may be made manually by an electric switch notshown here. The driver has this opportunity of by-passing so as toensure that the maximum brake pressure always can be provided to thebrake of the trailer vehicle.

Zero adjustment of the force sensitive transducer and the accelerometeris made after mounting the device in the vehicle by pushing apush-button switch, the present value of the signals from saidtransduser and accelerometer then being stored in the central unit 11 aszero value. The zero adjustment of said transduser is then madeautomatically and continuously.

I claim:
 1. A method for controlling an operating brake pressure topressure medium brakes arranged in a vehicle combination, said vehiclecombination comprising a tractor vehicle with a driver and at least onetrailer vehicle, said vehicles being connected by a conventionalcoupling device, and wherein said driver of said tractor vehiclegenerates by a brake valve, an operating pressure determining saidoperating brake pressure for said tractor and trailer vehicles, andwherein forces arising in said coupling device measured by a forcesensitive transducer during braking and are reduced by an electricallycontrolled valve to a predetermined force valve, comprising the stepsof:measuring said operating pressure with a pressure sensitivetransducer and converting it into an electric signal; recording with anaccelerometer any longitudinal inclination of said tractor vehicle andany acceleration and deceleration, respectively, of said vehiclecombination; controlling said operating brake pressure when saidoperating pressure measured exceeds a predetermined pressure value, saidrecorded longitudinal inclination is below a predetermined inclinationvalue, and said deceleration exceeds a predetermined deceleration value,said controlling of said operating brake pressure being achieved byopening and closing said electrically controlled valve, therebyadjusting said electric signal to decrease said forces, and by storingin a central unit an adjustment setting of said controlled pressure soas to be an initial adjustment setting at a subsequent braking.
 2. Themethod according to claim 1, characterized in that a value of saidforces during normal driving conditions in said coupling are measured insaid force sensitive transducer, and that said measured value of saidforces is utilized as a preference value at continuous zero adjustmentsof said force sensitive transducer.
 3. The method according to claim 2,characterized by initiating all braking procedures by opening completelysaid brake valve during a short impulse.
 4. The method according toclaim 1, characterized by initiating all braking procedures by openingcompletely said brake valve during a short impulse.
 5. The methodaccording to claim 4, characterized by inhibiting said adjustmentsetting of said operating brake pressure when a parking brake of saidtractor vehicle is activated.
 6. A device for controlling an operatingbrake pressure to pressure medium brakes arranged in a vehiclecombination, said vehicle combination comprising a tractor vehicle andat least one trailer vehicle, said vehicles being connected by aconventional coupling, comprising;a force sensitive transducer mountedin said coupling to measure forces arising in said coupling; a centralunit (11) operatively connected to said transducer; a brake pedal valve(12), a primary side thereof being connected to a supply container (15),and a secondary side thereof being connected to brakes (18A-18D) of saidtractor vehicle; an electrically controlled valve (14) having a primaryside and a secondary side; converting means (20) connected to saidsecondary side of said brake pedal valve (12) to record an operatingpressure and to convert said pressure to an electric signal; and means(13) provided to record any longitudinal inclination of said tractorvehicle and acceleration and deceleration, respectively, of said vehiclecombination; wherein said primary side of said electrically controlledvalve (14) is connected to said supply container (15), said secondaryside of said electrically controlled valve (14) being connected to saidbrakes (16A-16D) of said trailer vehicle, and wherein said central unitis operatively connected to said electrically controlled valve (14) andis constructed to start a control procedure when said operating pressureexceeds a predetermined pressure value, when said longitudinalinclination recorded is below a predetermined inclination value, andwhen said deceleration exceeds a predetermined deceleration value, andwherein said central unit (11) is arranged to store an adjustmentsetting of said operating pressure, said setting being utilized as aninitial setting at a subsequent braking.
 7. The device according toclaim 5, wherein said central unit is operatively connected to a controlmeans for a parking brake of said tractor vehicle and is arranged toreset said adjustment setting to a non-controlled value when saidparking brake is activated.